Modulating



R. A. HElSlNG 1 V MODULATIING J Original Filed p 21, 1915 Rc mok'id AHe/B P1 flw My Patented Oct. 19, 1926.

UNITED ATENT oFF'Ic RAYMOND A. HEIsING, on Basic ORANGE, NEW JnnsEm-Assro'Non To wnsrnnn annornrc COMPANY, INconrona'rnn, on N W YORK, N, Y., A. conronA'rIoN on NEW YORK.

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Original applicationfiled September 21, 1915, Serial No. 51,761. Yatent 1T0. 1,3e3,5B2, d ated Julie 15,

' 1920. Divided and this application filed June 4, 1920.. Serial 110,386,452.

This invention relates to systems for and methods of producing waveswhose amp11-- tude varies in accordance with other waves of lower frequency. Such systems are used in telephony and other wave' transmission and are commonly known as modulating Osgs terns because the waves roducedare m lated or varied in accor ance with a signaling wave. Y Q. v.

In a preferred form, the lnvention comprises an oscillation generator of the thermionic type, having a space current or discharge path between a heated filamentary or other cathode, and an anode, together with a discharge controlling element or electrode for controlling thedischarge .between the cathode and the anode. The usual form of control element is a grid-like structure between the cathode and the anode but the form and position of this elementmay vary. U. S. Patent to Colpitts, 1,137,384, granted A ril 27, 1915, is an illustration of this type of modulator. 'In this patent an arrangement is shown whereby high frequencyoscillations are caused to vary in amplitude in accordance with the speech frequency varia- :tions of potential impressed upon the grid.

The present invention comprises certain improvements in devices of this type.

In the arrangement herein disclosed modulation of the high frequency oscillations is produced by causing variations in the unidirectional voltage impressed between the anode and the cathode of the. oscillator.

frequency variations are caused to occur in both the input and output circuits of the oscillating tube. This is accomplished by providing a microphone, which is; a typical form of. variable-impedance device, in a path common to the input and output circuits. The variable impedance ofwthe microphone when it is acted upon 'by sound waves acts to vary-the effective voltage impressed upon the tube b', the space current "source, since it is locate ina series path containing the space current source rand the anodecathode pathoffthe tube.

The microphone also acts as an impedance to the high frequency .waves generated by the system, which impedance varies in accordance with thesound waves'acting there- 7 claims.

tween the cathode and the anode.

The circuit is so arranged that similar low- 'vention is not llmited to .the specific circuit" arrangement herem shown anddescribed, but

may be employed in various circuit arrangements within the scope of the appended I i For a detailed description of the circuit used, reference is made to the appended drawing,'wherein is shown a't uned circuit, comprising inductance 13 and variable ca pacity 14 connected to a discharge dev ice comprising an evacuated vessel 15, containing a heated filamentary cathode 16, a discharge controlling element 17, and an anode 18.- The discharge tube is supplied with space current by the source 20, which is connected in a path external to the tube be- The input circuit of the tube comprises a path external to the tube between the cathode and the control electrode. while the output circuit comprises a path between the cathode and the anode. The frequency of the oscillations set up will be principally determined by the magnitude of the self inductance 13 and the capacity 14:, while the'resistance 35, includedlin the tuned circuit, maybe so adjusted as to bring the oscilla tions we small amplitude. The advantage of this'is that when the amplitude of the osto an. intermediate point in the inductance 13, as is common lncircuits of this type. In'this connection are included a resistance 30in series with a battery 31, around both of which is connected a microphone 32. The battery 31 supplies energizing current to themicrophone 32 through the resistance -30, The battery 31, as shown, is connected with respect to the space current path of the tube in the same direction as the battery 20. The electromotive force of the battery 31, the ohmic value of the resistance 30, and the impedance of the microphone may vary through a wide range of values, but will in general, betjchosen' so as to give the best results withthe particular discharge tube in use, the characteristics of different types of tubes being widely different.

It will be seen that the microphone is in a series path containing the source and the discharge path of the tube. Hence, as the impedance of the microphone for unidirectional current varies, a corresponding varying electromotive force will be impressed across the tube between the cathode and the anode. Likewise, as the impedance of the microphone for high frequency currents varies, the energy supplied to the oscillatory circuit 13, 14 will be caused to further vary, since the varying current representingthis energy must flow through the path comprised by the microphone 32 in shunt to the resistance 30, the effective resistance of which path varies as the resistance of the microphone varies.

Coupled to the inductance 13 may be any device for utilizing the modulated oscillations roduced, but inpractice it will, in

genera be desirable to amplify these oscil-' lations. In the present instance the inductance 23 is included in the input circuit between the cathode 24 and-the grid 25 of a thermionic amplifier 22 of which the elements are enclosed inan evacuated vessel 26. The outputcircuit of tlie'am lifier extends from the cathode to the ano e 27 and contains a tuned circuit including capacity 28 and inductance 29. This tuned circuit is preferably adjusted to be resonant to the frequency set up by the oscillator. Coupled to inductance 29 is the coil 12 included in an antenna circuit 1 grounded at 11. The antenna circuit serves to radiate the amplified modulated oscillations."

For wire signaling the antenna circuit will be replaced by the usual conductive line.

The subject matter of this specification is divided from applicants Patent No.

1,343,562, filed September 21, 1915, granted June 15, 1920. The novel features believed to be inherent in the invention are defined in the appended claims.

WVhat is claimed is: 1. A wave generating system comprising a space discharge device having an anode,

a cathode, and an impedance control element, input and output circuits for said device, energy transfer means connecting said input and output circuits, a source of space current in series withsaid anode and cathode, means for varying the generated waves comprising a device whose impedance is controlled by and in accordance with sound waves in series, as regards the flow of said transferred energy, with said source external to said device.

2. A wave generating and transmitting system comprising a space discharge device having an anode, a cathode, and an impedance controlling element, input and output circuits for said device, means intercoupling said circuits, said input and said output circuits including a commonportion, means for varying the generated waves comprising an impedance serially included in said common portion, and means in shunt to said impedance for controlling the fall of potential therethrough in accordance with waves of lower frequency.

3. A wave generating system comprising a space discharge device having an input circuit between a cathode and an impedance controlling element, a loop circuit, a lead from said cathode to said loop circuit, and

- emitting cathode, an anode, and a grid element, a tuned circuit containing inductance and capacity, means connecting said device to said tuned circuit whereby oscillations are set up in said tuned circuit; a conductive path connecting said'device and said tuned circuit,'said path constituting a part of a complete circuit which is coupled to a portion ofsaid-timed circuit and which includes a space Within said device, and means conductively connected in said path .for varying the impedance thereof in accordance with signaling waves.

5. In a signaling system, the combination of an electron discharge device having an electron emitting cathode, an anode, and a grid element, a tuned circuit containing an inductance and a capacity connected at its terminals to the grid and the anode of said device, a path conductive to high'freq'uency current connecting the cathode of said device to said tuned circuit,-and means conductively connected in said path for varying the impedance of said path in accordance with signaling waves.

6. A modulating system comprising a tuned circuit,a discharge tube having input and output circuits connected to said tuned circuit for the generation of oscillations therein, an electron emitting cathode and an anode in said tube, a source of space current in series with said cathode and anode, and means whose impedance varies in response to sound waves connected in conductive relation with said source and said cathode.

7. A modulating system including a dis charge tube having an anode, a cathode and a grid, a circuit between said anode and cathode including a source of energy, a

microphone connected conductively in' said circuit, a high frequency input circuit connected to said cathode, a high frequencyoutput circuit connected to said anode, and an energy transferring coupling between said circuits;

8. An oscillation generating system comprising a space disc arge device having an anode, a cathode, and a grid, circuit arrangements connected to said device for the generation of oscillations thereby including a-grid circuit, an anode circuit, and a circuit for determining the frequency of the oscillations, a space current path external to said device between said anode and cathode including a source of .BlGClZIOI HOt'lVQ force, and a device conductively connected in said path whose impedancevaries in response to sound waves acting thereon.

9. Apparatus for producing a modulated wave which comprises a source of energy for producing unidirectionalcurrent, a device supplied with current :from sald source for converting the energy-of the supplied unidirectional current 1nto oscillations, acouductive circuit through which said'current flows, a'conductive' circuit through which at least a portion of said oscillations flows, an

impedance-containing element common to said circuits, and a device for.vary1ng the impedance which said impedance-containing element offers to the flow of said current and to the flow of said oscillations in accordance with a modulating force according to which said wave is .to be modulated.

10. A modulating s stem including a space discharge devlce, aving an anode, a cathode and a grid and said cathode, a path conductive to direct current between said anode and said cathode, and a sound wave controlled variable impedance conductively connected in said first mentioned path.

11. In a transmitting system, a work circuit, and means for generating and transmit ting the generated oscillations to said work circuit comprising an evacuated vessel containing. grid,-plate and filament electrodes, a circuit connecting said grid electrode with said filament electrode, a circuit connecting said grid electrode with said plate electrode,

id, a path symmetrically conductive to direct current between said.

and a signalling device conductively included in'said grid filament circuit.

12. In atransmitting system, a work circuit, and means for generating and transmitting the generatedoscillati'ons to said work circuit comprising an evacuated vessel containing grid, plate and filament electrodes, a

circuit vconnecting said grid electrode with said filament electrode, a jcircuit connecting said grid electrode with'said. plate electrode, and a device whose impedance for both direct and alternating current of the frequency electrode'rwithsaid cathode electrode, a circuit connectin said gridelectrode with said anode electro e, and a microphone conductively included in said grid-cathode circuit. 14. In an electrical signaling system, an evacuated vessel containing two cold electrodes and one hot electrode, an oscillating circuit comprising an inductance and a ca pacity in parallel which is connected across two of said electrodes, a tap connection between an intermediate pointof said circuit and the third electrode, said point' being separated from each of said two last-mentionedelectrodes by impedance means, and a signal transmitting device included in said connection. 1 v I 15. Inan electrical signaling system, anevacuated vessel contaimn trodes and one hot electro e, an oscillating circuit comprising an inductance and a capacity in parallel connected across two of said electrodes, a tap connection between an intermediate oint of said circuit and the third electro e, a signaling device in said connection, and a path other than said tap connection between two of said electrodes including a source of current. I I

In witness whereof, I hereunto subscribe my name this 27th dayof May A. D.,.1920.

, RAYMOND AQHEISING;

so" two cold elec- 

